As nigh-indispensable as Mac OS’s Software Update feature can be to locate and install patches for the operating system and supported applications from Apple, there remains the fact that some items might not install or the updater may not seem to work at all.
Per MacFixIt, a user identified as “The Dragon” posted this comment over in the Apple Discussion Boards:

“After a longish while, the “Checking for new software…” progress bar [in Software Update] had reached about halfway, and the update list indicated it had found five updates. At that point however, the progress bar chose to freeze entirely. After a good while and no further progress, I Cancel the update, and attempt to relaunch. Software Update opens, but the aforementioned progress bar freezes immediately.”

Like any other application, problems can occur if any required resources have become corrupt. From here, the application will start properly and not run correctly. These resources can include the program’s preferences files and caches. In addition, when updates are applied, a receipt is generated that Software Update reads to know what updates have already been installed. If an installation fails, but the receipt is left, software update may not try to install a needed update. Additionally, if a receipt is corrupt, then software update may try to repeatedly install the same update.
Assorted fixes for the issue include the following steps:

Fixes:
1. Remove Software Update preference and cache files.
If Software Update seems to be unable to complete an update, and either freezes or quits half-way through checking for updates, then try removing the application’s preferences and cache files from the following locations:
/username/Library/Preferences/ByHost/ –> remove “com.apple.SoftwareUpdate.NUMBER.plist”
/username/Library/Preferences/ –> remove “com.apple.SoftwareUpdate.plist”
/username/Library/Caches/ –> remove “com.apple.SoftwareUpdate” (folder)
/Macintosh HD/Library/Preferences/ –> remove”com.apple.SoftwareUpdate.plist”
After removing these items, restart the system for the changes to take effect and try launching Software Update again.
2. Remove faulty receipts.
If an update continuously appears and is being applied, try removing the receipt for that specific update. The receipt should be located in the /Macintosh HD/Library/Receipts/ folder and will be named something similar to the update files (i.e., FrontRowUpdate2.1.7.pkg). Do not delete the receipt, but instead move it to the desktop or some other location and retry the update. If it still does not work, replace the receipt in its original location, since it may be required and isn’t the root of the problem.

As nigh-indispensable as Mac OS’s Software Update feature can be to locate and install patches for the operating system and supported applications from Apple, there remains the fact that some items might not install or the updater may not seem to work at all.
Per MacFixIt, a user identified as “The Dragon” posted this comment over in the Apple Discussion Boards:

“After a longish while, the “Checking for new software…” progress bar [in Software Update] had reached about halfway, and the update list indicated it had found five updates. At that point however, the progress bar chose to freeze entirely. After a good while and no further progress, I Cancel the update, and attempt to relaunch. Software Update opens, but the aforementioned progress bar freezes immediately.”

Like any other application, problems can occur if any required resources have become corrupt. From here, the application will start properly and not run correctly. These resources can include the program’s preferences files and caches. In addition, when updates are applied, a receipt is generated that Software Update reads to know what updates have already been installed. If an installation fails, but the receipt is left, software update may not try to install a needed update. Additionally, if a receipt is corrupt, then software update may try to repeatedly install the same update.
Assorted fixes for the issue include the following steps:

Fixes:
1. Remove Software Update preference and cache files.
If Software Update seems to be unable to complete an update, and either freezes or quits half-way through checking for updates, then try removing the application’s preferences and cache files from the following locations:
/username/Library/Preferences/ByHost/ –> remove “com.apple.SoftwareUpdate.NUMBER.plist”
/username/Library/Preferences/ –> remove “com.apple.SoftwareUpdate.plist”
/username/Library/Caches/ –> remove “com.apple.SoftwareUpdate” (folder)
/Macintosh HD/Library/Preferences/ –> remove”com.apple.SoftwareUpdate.plist”
After removing these items, restart the system for the changes to take effect and try launching Software Update again.
2. Remove faulty receipts.
If an update continuously appears and is being applied, try removing the receipt for that specific update. The receipt should be located in the /Macintosh HD/Library/Receipts/ folder and will be named something similar to the update files (i.e., FrontRowUpdate2.1.7.pkg). Do not delete the receipt, but instead move it to the desktop or some other location and retry the update. If it still does not work, replace the receipt in its original location, since it may be required and isn’t the root of the problem.